Materials testing machine grips for thin sheet material



- July 28, 1959 A N s 2,896,448

' MATERIALS TESTING MACHINE GRIPS FOR THIN SHEET MATERIAL Filed Oct 11,1956 INVENTOR LEW/S 6. HAINES A r TORNEY United States Patent TESTINGMACHINE GRIPS FOR THIN SHEET MATERIAL Lewis G. Haines, Washington, Pa.

Application October 11, 1956, Serial No. 615,346

2 Claims. (Cl. 73-103) This invention relates to grips for thin sheetmetal specimens subject to tensile testing.

Various types of grips have been proposed and used for holding thinsheet metal specimens when subjected to tensile test loads but generallysuch grips required a wedging action that distributed the stress sounevenly as to produce undesirable fractures on thin specimens. Theprior art has also had other deficiencies either structurally,functionally or economically.

It is an object of my invention to provide an improved grip for testingthin sheet metal specimens so as to distribute the stress evenly overthe entire cross section of the specimen whereby tests of a high orderof reliability in accuracy and reproducibility can be obtained.

A further object is to provide a grip for thin sheet metal tensilespecimens that is relatively simple and economical in construction,operation and maintenance and does not in any way sacrifice the desiredreliability and characteristics above mentioned.

Other objects and advantages will be more apparent to those skilled inthe art from the following description of the accompanying drawings inwhich:

Fig. 1 is an elevational view of my improved grips disposed in materialstesting machine platens;

Fig. 2 is a sectional View taken substantially on the line 22 of Fig. 3and showing one end of a specimen in its initially inserted unclampedposition;

Fig. 3 is a sectional view taken substantially on the line 3-3 of Fig.2;

Fig. 4 is an enlarged side view of my grip showing a gripping pin insection with the specimen shown at the beginning of its gripping action;

Fig. 5 is a view similar to Fig. 4 but showing the specimen in itscompletely clamped position; and

Fig. 6 is a section taken substantially on the line 66 of Fig. 2.

In the particular embodiment of the invention disclosed herein I haveshown upper and lower specimen loading platens 1 and 2. of any usualmaterials testing machine in which loading rods 3 and 4 are mountedwithin usual swivel joints 5. The holders 3 and 4 are threadedlyconnected to upper and lower grip bodies 6 and 7. Inasmuch as the gripsare identical, except for extending toward each other, it will sufliceto describe only one. The grip body has a transverse cylindrical opening8 while a slot it extends upwardly from a curved lower end 10 forcommunication with the opening. A short aligned continuation 11 of theslot 9 extends from the other side of the opening. A pin 12 of smallercross sectional area, i.e., diameter, than the opening and ofsubstantially the same length thereof is provided with a slot 13disposed diametrically and extending the length of the pin. This slot issubstantially the same width as the body slots 9 and 11 so as to permitthe end of a sheet metal specimen 15 to extend upwardly to the depth ofthe short slot 11 whereupon the pin 12 is rotated so as to bend the end16 of the specimen in a position shown in Fig. 4 and to start pullingthe specimen within the space between the pin 12 and the lower side ofhole 8. The pin 12 is rotated until its full gripping position isobtained, as shown in Fig. 5, at which time the specimen portion 16overlaps another portion of the specimen. However, under certainconditions it may be sufficient to merely rotate the specimen to apartial position. It is thus seen that the space between the pin andopening is determined by the thickness of the specimen.

Rotation of the pin 12 is effected by a, shaft continuation 17 of thepin and whose diameter is preferably substantially equal to that of theopening 8. A knurled knob 18 is slidable axially on shaft 17 and impartsrota-.

tion thereto by a suitable longitudinal spline 19. A pair of lockingpins '20 extend inwardly from knob 18 and after rotation of the slottedpin to its gripping position the knob 18 is moved along the shaft 17 tocause the pins 20 to enter fully a set of openings 21 or 22 dependingupon the angular position of the knob, thereby to prevent reverserotation of the slotted pin during loading. When the specimen issimilarly gripped in the lower grip body 7 a load may be applied to thespecimen.

Because of my improved gripping action there is no wedging action andthe stress is distributed so evenly over the entire cross section of thespecimen that in many cases full cup type fractures are obtained onmaterial as thin as .002 inch in thickness. It is also seen that thedevice is extremely simple in operation and is economical in manufactureand maintenance.

It will, of course, be understood that various changes in details ofconstruction and arrangement of parts may be made by those skilled inthe art without departing from the spirit of the invention as set forthin the appended claims.

I claim:

1. A specimen grip for holding sheet material to which load is appliedin a straight line direction lengthwise of that portion of the sheetunder test comprising, in combination, a grip body having a transverseopening therein, of substantially circular cross section and having aspecimen receiving slot therein extending from one end of the body tothe opening substantially radially thereof and lying in the plane of thelengthwise portion of the sheet under test, a pin disposed within saidopening about the axis thereof and being of less cross sectional areathan the opening so as to provide a space within which an end portion ofthe specimen may be drawn, said pin having a substantially radial slotwhich in one position is in alignment with the body slot so as toreceive a specimen, and means for rotating said slotted pin so that aportion of the specimen is drawn within said space between the pin andopening.

2. The combination set forth in claim 1 further characterized in thatthe body has a continuing slot substantially diametrically opposite tosaid other slot so as to receive the end of a specimen when initiallyinserted in the grip whereby said specimen end is bent over onto the pinupon rotation thereof.

References Cited in the file of this patent UNITED STATES PATENTS1,272,944 Green July 16, 1918 2,293,084 Sedam Aug. 18, 1942 2,704,466Way Mar. 22, 1955 FOREIGN PATENTS 294,447 Great Britain July 26, 1928

